Two aspects of gonadotropin secretion in the male will be studied. The release of gonadotropin-releasing hormone (GnRH) will be studied using the incubated rat hypothalamus. We have already described a system for measuring the release of GnRH from the incubated rat hypothalamus. GnRH release in this system can be stimulated by membrane depolarization and inhibited by blocking calcium uptake. Three areas of potential influence on GnRH release will be investigated: 1) gonadal steroids, 2) prolactin, and 3 neurotransmitters. The control of FSH secretion in men who have pituitary adenomas associated with selective FSH hypersecretion will also be studied. This abnormality is relatively common: 12 of 50 men with pituitary adenomas whom we have recently reported have this abnormality. Preliminary studies suggest that the FSH hypersecretion is due to abnormal control of FSH secretion by a gonadotroph cell adenoma. The objective of this phase of the study is to elucidate further the mechanism of selective FSH hypersecretion by determining if 1) FSH and LH respond to stimuli to which they normally do not, such as thyrotropin-releasing hormone (TRH); 2) the elevated serum FSH concentration can be suppressed by testosterone as readily as in men who have primary hypogonadism; 3) the control of the FSH beta subunit and the FSH alpha subunit are abnormal; and 4) control of FSH secretion by these adenoma cells is abnormal in vitro (tissue culture), as well as in vivo.